1. Field of the Invention
The present invention relates to a fuel supply control apparatus for an internal combustion engine, and more particularly to a fuel supply control apparatus which detects by an air flow sensor an air intake quantity into the internal combustion engine to thereby control an optimum fuel supply to the internal combustion engine by means of optimal filtering on the basis of the detected value of air intake quantity.
2. Description of the Prior Art
For fuel control of the internal combustion engine, an air flow sensor (to be hereinafter called AFS) is provided at the upstream side of a throttle valve so that an air intake quantity per one suction is obtained by the information from the AFS and the number of revolutions of the engine, thereby controlling the fuel supply quantity on the basis of the above data.
In a case where the AFS is disposed at the upstream side of the throttle valve in the air intake passage so as to detect an air intake quantity into the internal combustion engine, the AFS, when the throttle valve abruptly opens, will measure even the quantity of air which does not reach the engine, being filled in the intake passage between the throttle valve and the engine. Therefore, the AFS measures an air quantity larger than that actually taken into the internal combustion engine so that a fuel quantity is controlled as it is, thereby creating inconvenience of resulting in overrich fuel. Hence, conventionally, when the output of AFS, that is, the detected air intake quantity at a predetermined crank angle, is represented by AN(t), the (n-1)th and (n)th air intake quantities into the internal combustion engine at the predetermined crank angle thereof are represented by AN(n-1) and AN(n) respectively, and the filter constant is represented by K, AN(n) is given in the following equation: EQU AN(n)=K1.times.AN(n-1)+K2.times.AN(t).
Hence, the obtained value of AN(n) may be used to carry out the fuel control, which has smoothened the air intake quantity at every predetermined crank angle to thereby perform proper fuel control.
The aforesaid proposal of the optimal filter is disclosed in the Japanese Patent Publication No. 60-60025 (1985).
In the aforesaid conventional apparatus, however, a delay of computation of the air quantity occurs by more, than duration of one suction because of the compensating computation of the air intake quantity, thereby varying an air fuel ratio to increase variation in the number of revolutions of engine during the idling, for example. Namely, in FIG. 1, (a) shows the number of revolutions of the engine: Ne, (b) shows intake pipe pressure, (c) shows a driving pulse width for an injector, and (d) shows the air fuel ratio. When the number of revolutions Ne varies, pressure in the intake pipe affected by a volume thereof somewhat delays in variation. The air quantity taken in the internal combustion engine also lags behind the number of revolutions of the engine Ne in comparison with the intake pipe pressure, and, when corrected by the aforesaid equation, further lags behind the intake pipe pressure, and the pulse width signal for the injectors lags as shown by (e) in FIG. 1(c). At this time, the air fuel ratio, as shown by (g) in FIG. 1, becomes rich under the influence of a surge tank accompanied by a rise of the number of revolutions of the engine and by a delay in computation, in other words, the ratio becomes smaller than 14.7. Therefore, an engine torque increases from the characteristic of internal combustion engine as shown in FIG. 2 and the number of revolutions Ne of the engine further rises. The,, the number of revolutions Ne of engine, when reaching the upper limit, turns to lowering, at which time the influence of the surge tank or the delay in computation makes the air fuel ratio thinner (larger than 14.7) to decrease the engine torque, thus further decreasing the number of revolutions Ne of the engine.
Thus, conventionally, the air fuel ratio varies in the direction of promoting the variation in the number of engine revolutions, thereby creating the problem in that the operating condition of the engine becomes very unstable.